How big should a kitten be?

My kitten was a little over 2 pounds when I got him at 3 months old, and the vet said that he was a little too thin at the time. He is now 7 months old and was 8 lbs 5oz at his last weigh in a couple of days ago. The vet has me bring him in frequently so that she can weigh him and make sure that he is continuing to gain weight since he is not able to be on kitten food (long story). She is glad that he is still gaining and wants him to keep getting bigger. Is she crazy? I don't think she will be happy until he reaches sumo wrestler size. I guess the rapid weight gain is normal for a growing kitten, but how big is too big? I thought the general rule was one pound per month or something. If that is the case, he is overweight, but the vet seems pleased with his progress. His feet are huge, so I am afraid that he may grow to be a small horse . He does not look fat right now, just really "built" and solid, if that makes sense. He is still adorable though--like a little kitten bodybuilder. He is going to overtake my female adult cat soon, who is a little under 10 pounds. I wonder what weight he is supposed to be before he stops growing.

Every cat is different.  I  have 3 cats.  One weighs 6 1/2 lbs (female).  One male weighs 9 lbs, the other weighs 13 1/2 lbs.  There are just like humans, it depends on their bone structure, how long their legs are, what their breed is, etc. 

I think I would rely on my Vet in this instance